A plasmid, pJL6, was constructed that contains a unique Cla I site twelve codons beyond the bacteriophage lambd cII gene initiation codon as well as an adjacent unique Hind III site. These sites allowed us to fuse the sequences from the avian myelocytomatosis virus (MC29) v-myc gene, the avian myeloblastosis virus (AMV) v-myb gene, and the Harvey murine sarcoma virus (Ha-MuSV) v-ras gene to the aminoterminal portion of the cII gene. Transcription of the hybrid genes is controlled from the lambda major leftward promoter. When this promoter is derepressed, Escherichia coli cells harboring the chimeric plasmid produce levels of fusion proteins that are greater than five percent of total cellular protein. Antibodies raised by the cII-myc fusion protein form an immunoprecipitate with the MC29 gene product, P110gag-myc. The cII-ras fusion protein is precipitated by monoclonal antibodies directed toward the Ha-MSV p21 (v-ras protein) binds GDP, and is capable of autophosphorylatin.